Hitherto, a drive shaft moving apparatus of this type is known for example in Japanese Unexamined Patent Publication No. Hei-5-180299, which, as illustrated in FIG. 7, includes drive shaft 53 with an outer circumferential surface on which ball screw groove 50 and ball spline groove 51 are respectively formed, ball screw nut 55 provided in engagement with the ball screw groove 50 and ball spline nut 56 provided in engagement with the ball spline groove 51. The respective nuts 55, 56 are supported on a main flame (not shown) via bearings in such a manner as to be rotatable or stoppable.
The drive shaft 53 is slid in the axial direction and hence moved forward and backward by the rotation of the ball screw nut 55. The ball spline nut 56 engaged with the ball spline groove acts to prevent the rotation of the drive shaft 53.
Such a conventional drive shaft moving apparatus has the ball screw nut 55 provided spaced apart from the ball spline nut 56. This arrangement requires separate spaces for accommodating the ball screw nut 55 and the ball spline nut 56 along the lengthwise direction of the drive shaft 53, and hence necessitates increase in size of a unit incorporated with this drive shaft moving apparatus. Particularly, this arrangement is disadvantageous for use in robots or the like, which are required to be downsized.
Accordingly, it is an object of the present invention to downsize the entire unit by replacing the conventional ball spline nut with a fixing means which is interposed between the ball screw nut and the drive shaft, thereby restraining the rotation of the drive shaft.